Process for the production of ethylene oxide

ABSTRACT

The invention relates to a process for the production of ethylene oxide, comprising the steps of producing ethylene resulting in a stream comprising ethylene and ethane; producing ethylene oxide by subjecting ethylene and ethane from the stream comprising ethylene and ethane to oxidation conditions resulting in a stream comprising ethylene oxide, unconverted ethylene and ethane; and recovering ethylene oxide from the stream comprising ethylene oxide, unconverted ethylene and ethane.

The present invention relates to a process for the production ofethylene oxide.

Ethylene oxide is used as a chemical intermediate, primarily for theproduction of ethylene glycols but also for the production ofethoxylates, ethanol-amines, solvents and glycol ethers. It is producedby the direct oxidation of ethylene with high-purity oxygen or air.Several processes for producing the ethylene starting material areknown. For example, it is known to steam crack hydrocarbon streams, suchas an ethane stream, a naphtha stream, a gasoil stream or a hydrowaxstream, into ethylene. Further, it is known to produce ethylene byoxidative dehydrogenation (oxydehydrogenation; ODH) of ethane. Yetanother way to produce ethylene is by conversion of an oxygenate, suchas methanol, into ethylene.

All these ethylene production processes have in common that before anysubsequent step wherein the ethylene is further converted into usefulchemical intermediates, the ethylene containing product stream has to bepurified. For example, the ethylene containing product stream has to befreed from ethane as the latter may interfere in any subsequent step, sothat a purified ethylene stream can be fed to the subsequent step, suchas the step of oxidation of ethylene. Said ethane may originate from thefeed for producing the ethylene. For example, the above-mentioned ethanesteam cracking and ethane oxydehydrogenation processes may result inproduct streams which still contain unconverted ethane in addition tothe desired ethylene product. Further, such ethane may originate fromethylene production processes wherein ethane is produced as aby-product. For example, in the above-mentioned naphtha, gasoil orhydrowax steam cracking and methanol to ethylene conversion processes,ethane is produced as a by-product. Separating ethane from an ethyleneproduct stream may be done by use of an ethylene/ethane splitter. Havingto separate ethane from the ethylene is very cumbersome and results in ahigh expenditure for producing ethylene and results in relatively highethylene losses.

Further, in case said purified ethylene stream not containing ethane isused to make ethylene oxide by oxidation, a ballast gas should be added.For in the oxidation of ethylene an oxidizing agent, such as high-purityoxygen or air, is required. In 1958, the direct ethylene oxidationprocess was modified by Shell to allow the use of high-purity oxygen,rather than air, as the oxidant. See: J. M. Kobe, W. E. Evans, R. L.June, and M. F. Lemanski, Encyclopedia of Catalysis, Istvan Horvath,Ed., Wiley-Interscience, v. 3, p. 246, 2003.

Because an oxidizing agent is required, it is important to control thesafe operability of the reaction mixture. Historically, nitrogen wasutilized as a ballast gas for the industrial epoxidation of ethylene.Over the past thirty years, the use of methane ballast has graduallyreplaced almost all commercial nitrogen-ballasted processes. Onefunction of a ballast gas is thus to control this safe operability.Ballast gases that can be used in the production of ethylene oxide byoxidation of ethylene, are thus nitrogen and methane. It is verycumbersome to provide such ballast gas and feed it to the ethyleneoxidation unit, which results in a high expenditure for producingethylene oxide.

An object of the present invention is to provide a process for theproduction of ethylene oxide by producing ethylene and then producingethylene oxide by oxidation of said ethylene, which process does nothave the above drawbacks.

Surprisingly, it was found that the above drawbacks are avoided by meansof an integrated process wherein ethylene is produced resulting in astream comprising ethylene and ethane, wherein ethylene and ethane fromthe latter stream are subjected to oxidation conditions resulting in thedesired ethylene oxide

Accordingly, the present invention relates to a process for theproduction of ethylene oxide, comprising the steps of:

producing ethylene resulting in a stream comprising ethylene and ethane;

producing ethylene oxide by subjecting ethylene and ethane from thestream comprising ethylene and ethane to oxidation conditions resultingin a stream comprising ethylene oxide, unconverted ethylene and ethane;and

recovering ethylene oxide from the stream comprising ethylene oxide,unconverted ethylene and ethane.

An advantage of the present invention is that no ethane has to beseparated from the ethylene containing product stream that results fromthe ethylene production step. This results in a much simpler overallprocess using less separation processes and equipment. In addition, thenon-separated ethane advantageously functions as a ballast gas in thenext ethylene oxidation step so that no or substantially less additionalballast gas needs to be added. Still further, separation of the streamcomprising ethylene and ethane resulting from the ethylene productionstep of the present process is advantageously automatically, and atleast partially, effected in the ethylene oxide production step whereinthe ethylene is consumed and converted into ethylene oxide which can beseparated more easily from the non-consumed ethane. All these and otheradvantages result in a substantial reduction of expenditure, for examplesavings on costs for compression, refrigeration, etc. needed forseparating ethane from the ethylene. These and other advantages arefurther described below.

GB1314613 discloses the use of ethane as a ballast gas in the productionof ethylene oxide from ethylene. However, the integrated process of thepresent invention is not disclosed and is neither suggested inGB1314613.

The ethylene oxidation step in the present process results in a streamcomprising ethylene oxide, unconverted ethylene and ethane. The ethyleneoxide can be recovered easily from such stream by means of methods knownto the skilled person. That is to say, ethylene oxide may be separatedfrom said stream comprising ethylene oxide, unconverted ethylene andethane resulting in a stream comprising unconverted ethylene and ethane.The unconverted ethylene and the ethane from the latter stream may berecycled within the present process and advantageously be converted andre-used, respectively, after such recycle. After ethylene oxide isseparated from said stream comprising ethylene oxide, unconvertedethylene and ethane and before such recycle of the remaining unconvertedethylene and ethane, any carbon dioxide is removed. That is to say,either part or all carbon dioxide is removed. Said carbon dioxide may beproduced in the ethylene oxide production step. Ways of removing carbondioxide, such as a caustic wash, are known to the skilled person.

Unconverted ethylene, and optionally ethane, from the stream comprisingethylene oxide, unconverted ethylene and ethane resulting from the stepof producing ethylene oxide may be recycled to that step of producingethylene oxide. That is to say, either part or all unconverted ethylene,and optionally ethane, is recycled in such way. The recycled unconvertedethylene is then advantageously converted as yet in that ethyleneoxidation step. Further, the recycled ethane is then advantageouslyre-used as a ballast gas in that ethylene oxidation step. In thisembodiment, preferably, a stream comprising unconverted ethylene andethane is separated from the stream comprising ethylene oxide,unconverted ethylene and ethane resulting from the step of producingethylene oxide, and is then recycled to the step of producing ethyleneoxide. Such recycle has both said advantages in that conversion ofunconverted ethylene into ethylene oxide is effected as yet, whereasre-use of ethane as a ballast gas is also effected at the same time.

In cases wherein ethylene is produced from a feed containing ethane inthe ethylene production step of the present process, ethane from thestream comprising ethylene oxide, unconverted ethylene and ethaneresulting from the step of producing ethylene oxide may also be recycledto the ethylene production step. In the latter embodiment, ethane fromthe stream comprising ethylene oxide, unconverted ethylene and ethane isrecycled to the step of producing ethylene. That is to say, either partor all ethane is recycled in such way. This embodiment has the advantagethat more ethylene may be produced by recycling unconverted ethanewhereas ethane that is still not converted after such recycle will thenautomatically be re-used as a ballast gas in the ethylene oxidationstep.

Further, in such cases wherein ethylene is produced from a feedcontaining ethane in the ethylene production step of the presentprocess, ethane from the stream comprising ethylene oxide, unconvertedethylene and ethane resulting from the step of producing ethylene oxidemay also be recycled to both the ethylene production step and theethylene oxide production step. In the latter embodiment, ethane fromthe stream comprising ethylene oxide, unconverted ethylene and ethane isrecycled to the step of producing ethylene and to the step of producingethylene oxide. This embodiment is illustrated in FIG. 1.

Where in the present specification reference is made to recycling to the“step of producing ethylene” or “ethylene production step”, or recyclingto the “step of producing ethylene oxide”, “ethylene oxide productionstep” or “ethylene oxidation step”, such steps not only cover thestep(s) of production of the desired product in question but also thestep(s) of work-up of the product stream in question.

In the flow scheme of FIG. 1, stream 1 comprising a feed containingethane is fed to ethylene production unit 2. Stream 3 comprisingethylene and ethane and stream 4 comprising an oxidizing agent, such ashigh-purity oxygen or air, are fed to ethylene oxide production unit 5.Stream 6 comprising ethylene oxide, unconverted ethylene, ethane andcarbon dioxide is sent to ethylene oxide separation unit 7. Ethyleneoxide is recovered via stream 8. Further, stream 9 comprisingunconverted ethylene, ethane and carbon dioxide is split into twosubstreams 9 a and 9 b. Substream 9 a is recycled to ethylene oxideproduction unit 5. Substream 9 b is fed to carbon dioxide removal unit10. Stream 11 comprising unconverted ethylene and ethane is split intotwo substreams 11 a and 11 b. Substream 11 a is recycled to ethyleneoxide production unit 5. Substream 11 b is fed to ethylene/ethaneseparation unit 12. Stream 13 comprising unconverted ethylene and stream14 comprising unconverted ethane are recycled to ethylene oxideproduction unit 5 and to ethylene production unit 2, respectively.Further, a third stream may be separated in ethylene/ethane separationunit 12, namely a top bleed stream comprising uncondensable components,such as oxygen and/or argon (said third stream not shown in FIG. 1).Still further, stream 3 may be subjected to hydrotreatment in ahydrotreater unit before entering ethylene oxide production unit 5 (saidhydrotreater unit not shown in FIG. 1) to convert any acetylene present.

An embodiment of the present invention, wherein ethane from the streamcomprising ethylene oxide, unconverted ethylene and ethane resultingfrom the step of producing ethylene oxide is not recycled to theethylene production step but only to the ethylene oxide production step,is illustrated in FIG. 2. In the latter embodiment, ethane from thestream comprising ethylene oxide, unconverted ethylene and ethane isonly recycled to the step of producing ethylene oxide. Such embodimentespecially applies advantageously to cases where during ethyleneproduction ethane is produced as a by-product, as for example in theabove-mentioned methanol to ethylene conversion process.

For an explanation of the flow scheme of FIG. 2, reference is made tothe above explanation of the flow scheme of FIG. 1, the only differencebeing that in the flow scheme of FIG. 2 stream 14 is not recycled toethylene production unit 2.

In the ethylene oxide production step of the present process, ethyleneoxide is produced by subjecting ethylene and ethane from the streamcomprising ethylene and ethane, originating from the ethylene productionstep, to oxidation conditions resulting in a stream comprising ethyleneoxide, unconverted ethylene and ethane.

An advantage of the present process is that the product stream resultingfrom the ethylene production step also comprises ethane, in addition toethylene that is to be oxidized in the next step. Ethane is a suitableballast gas in the oxidation of ethylene. As discussed above, normallynitrogen or methane is added as a ballast gas in the oxidation ofethylene. Now that in the present invention, ethane present in theethylene containing product stream resulting from the ethyleneproduction step functions as a ballast gas in the ethylene oxideproduction step, no or substantially less of a separate ballast gas,such as nitrogen or methane, has to be added. This results in a muchsimpler and more efficient ethylene oxidation process.

In the present invention, additional ballast gas, such as nitrogen ormethane, may be added to the ethylene oxide production step. However, itis also envisaged in cases wherein ethylene is produced from a feedcontaining ethane in the ethylene production step of the presentprocess, that the conversion in the ethylene production step is tuneddepending on the desired amount of ballast gas needed in the ethyleneoxide production step. That is to say, in case the demand for ballastgas in the ethylene oxide production step is relatively low, conversionin the ethylene production step may be set higher such that relativelyless unconverted ethane is present in the product stream resulting fromthe ethylene production step. And, conversely, in case the demand forballast gas in the ethylene oxide production step is relatively high,conversion in the ethylene production step may be set lower such thatrelatively more unconverted ethane is present in the product streamresulting from the ethylene production step. Alternatively, conversionin the ethylene production step may be kept constant and additionalballast gas, such as nitrogen or methane, may be added to the ethyleneoxide production step, as mentioned above. For example, the conversionin the ethylene production step of the present process may range from 5to 90%, suitably from 10 to 60%.

In the ethylene oxide production step of the present process, ethyleneand ethane from the stream comprising ethylene and ethane are contactedwith an oxidizing agent. The oxidizing agent may be high-purity oxygenor air, but is preferably high-purity oxygen which may have a puritygreater than 90%, preferably greater than 95%, more preferably greaterthan 99%, and most preferably greater than 99.9%. Typical reactionpressures are 1-40 bar, suitably 10-30 bar, and typical reactiontemperatures are 100-400° C., suitably 200-300° C.

Further, the amounts of ethylene and ethane, respectively, as fed to theethylene oxide production step of the present process, may be of from 10to 90 wt. %, suitably of from 20 to 80 wt. % of ethylene, and 90 to 10wt. %, suitably of from 80 to 20 wt. % of ethane, respectively, all saidamounts based on the total amount of the stream or the streamscomprising ethylene and/or ethane as fed to said ethylene oxideproduction step.

The minimum amount of ethylene as referred to above may be 1 wt. %, 5wt. %, 10 wt. %, 20 wt. %, 25 wt. %, 30 wt. % or 35 wt. %. The maximumamount of ethylene as referred to above may be 99 wt. %, 95 wt. %, 90wt. %, 80 wt. %, 70 wt. %, 60 wt. %, 55 wt. %, 50 wt. % or 45 wt. %. Theminimum amount of ethane as referred to above may be 1 wt. %, 5 wt. %,10 wt. %, 20 wt. %, 25 wt. %, 30 wt. % or 35 wt. %. The maximum amountof ethane as referred to above may be 99 wt. %, 95 wt. %, 90 wt. %, 80wt. %, 70 wt. %, 60 wt. %, 55 wt. %, 50 wt. % or 45 wt. %.

Further, it is preferred that in the ethylene oxide production step ofthe present process, the ethylene and ethane are contacted with acatalyst, preferably a silver containing catalyst. A typical reactor forthe ethylene oxide production step consists of an assembly of tubes thatare packed with catalyst. A coolant may surround the reactor tubes,removing the reaction heat and permitting temperature control.

In case a silver containing catalyst is used in the ethylene oxideproduction step of the present process, the silver in the silvercontaining catalyst is preferably in the form of silver oxide. Preferredis a catalyst comprising particles wherein silver is deposited on acarrier. Suitable carrier materials include refractory materials, suchas alumina, magnesia, zirconia, silica and mixtures thereof. Thecatalyst may also contain a promoter component, e.g. rhenium, tungsten,molybdenum, chromium, nitrate- or nitrite-forming compounds andcombinations thereof. Preferably, the catalyst is a pelletized catalyst,for example in the form of a fixed catalyst bed, or a powdered catalyst,for example in the form of a fluidized catalyst bed.

The nature of the ethylene oxidation catalyst, if any, is not essentialin terms of obtaining the advantages of the present invention asdescribed herein. The amount of the ethylene oxidation catalyst isneither essential. If a catalyst is used, preferably a catalyticallyeffective amount of the catalyst is used, that is to say an amountsufficient to promote the ethylene oxidation reaction. Although aspecific quantity of catalyst is not critical to the invention,preference may be expressed for use of the catalyst in such an amountthat the gas hourly space velocity (GHSV) is of from 100 to 50,000 hr ¹,suitably of from 500 to 20,000 hr⁻¹, more suitably of from 1,000 to10,000 hr ¹, most suitably of from 2,000 to 4,000 hr⁻¹.

In the present specification, “GHSV” or gas hourly space velocity is theunit volume of gas at normal temperature and pressure (0° C., 1atmosphere, i.e. 101.3 kPa) passing over one unit volume of catalyst perhour.

A moderator, for example a chlorohydrocarbon such as monochloroethane(ethyl chloride), vinyl chloride or dichloroethane, may be supplied forcatalyst performance control in the ethylene oxide production step ofthe present process. Most suitably, ethyl chloride is used.

Moderators that can be suitably used in the ethylene oxide productionstep of the present process are also disclosed in above-mentionedGB1314613, the disclosure of which is herein incorporated by reference.GB1314613 discloses the use of an inhibitor (that is to say, amoderator), selected from ethylene dichloride, vinyl chloride,dichlorobenzene, monochlorobenzene, dichloromethane, and chlorinatedphenyls, chlorinated biphenyls and chlorinated polyphenyls, in theproduction of ethylene oxide from ethylene.

The nature of the moderator, if any, is not essential in terms ofobtaining the advantages of the present invention as described herein.The amount of the moderator is neither essential. The amount of suchmoderator in the reaction mixture may range from 1 part per million byvolume (ppmv) to 2 vol. %, suitably 1 to 1,000 ppmv. The minimum amountof moderator in the reaction mixture may be 0.1 ppmv, 0.2 ppmv, 0.5ppmv, 1 ppmv, 2 ppmv, 5 ppmv, 10 ppmv or 50 ppmv. The maximum amount ofmoderator in the reaction mixture may be 2 vol. %, 1 vol. %, 1,000 ppmv,800 ppmv or 700 ppmv.

A suitable range for the amount of moderator that can be used in theethylene oxide production step of the present process is also disclosedin above-mentioned GB1314613 in relation to the above-mentioned group ofspecific inhibitors (that is to say, moderators) as disclosed in saidGB1314613, the disclosure of which is herein incorporated by reference.

Examples of ethylene oxidation processes, including catalysts and otherprocess conditions, are for example disclosed in US20090281345 andabove-mentioned GB1314613, the disclosures of which are hereinincorporated by reference. All of these ethylene oxidation processes aresuitable for the ethylene oxidation step of the present invention.

In accordance with the present invention, the process for producingethylene in the ethylene production step may be any process as long asit results in a stream comprising ethylene and ethane. One example ofsuch process is a process for steam cracking hydrocarbon streams, suchas an ethane stream, a naphtha stream, a gasoil stream or a hydrowaxstream, into ethylene. The product stream resulting from such steamcracking process will always contain, in addition to the ethyleneproduct, some unconverted ethane and/or ethane by-product.

In the present specification, “naphtha” refers to a mixture comprisingsaturated hydrocarbons which have a boiling point ranging from 20 to200° C. Generally, said hydrocarbons have between 5 and 12 carbon atoms.Further, “gasoil” refers to a mixture comprising saturated hydrocarbonswhich have a boiling point ranging from 200 to 600° C., and “hydrowax”refers to a mixture comprising saturated hydrocarbons which have aboiling point ranging from 250 to 700° C.

The steam cracking process is performed at elevated temperatures,preferably in the range of from 650 to 1000° C., more preferably of from750 to 950° C. The conversion is typically in the range of from 40 to 75mol %, based on the total number of moles of hydrocarbon provided to thecracking zone. Hydrocarbon stream steam cracking processes are wellknown. Reference is for instance made to Kniel et al., Ethylene,Keystone to the petrochemical industry, Marcel Dekker, Inc, New York,1980, in particular chapter 6 and 7.

Hereinbelow, the present invention and its advantages are furtherillustrated with reference to a process wherein the ethylene is producedby oxidative dehydrogenation (oxydehydrogenation; ODH) of ethane.

In one embodiment, the present invention relates to a process for theproduction of ethylene oxide, comprising the steps of:

producing ethylene by subjecting a stream comprising ethane tooxydehydrogenation conditions resulting in a stream comprising ethyleneand unconverted ethane;

producing ethylene oxide by subjecting ethylene and unconverted ethanefrom the stream comprising ethylene and unconverted ethane to oxidationconditions resulting in a stream comprising ethylene oxide, unconvertedethylene and unconverted ethane; and

recovering ethylene oxide from the stream comprising ethylene oxide,unconverted ethylene and unconverted ethane.

Preferably, in the above-mentioned ethane oxydehydrogenation embodiment,a stream comprising unconverted ethylene and unconverted ethane isseparated from the stream comprising ethylene oxide, unconvertedethylene and unconverted ethane and is recycled to the step of producingethylene oxide. Further, preferably, said separated stream comprisingunconverted ethylene and unconverted ethane is further separated into astream comprising unconverted ethylene which is recycled to the step ofproducing ethylene oxide and a stream comprising unconverted ethanewhich is recycled to the step of producing ethylene.

In addition, advantageously, the latter separation is not critical sothat a complete separation of ethane from ethylene is not needed. In theethane oxydehydrogenation embodiment of the present invention, ethane isboth starting material in the ethylene production step and ballast gasin the subsequent ethylene oxide production step. All that matters isthat the separated substream which comprises more ethylene than theother separated substream is recycled to the step of producing ethyleneoxide, whereas the other separated substream is recycled to the step ofproducing ethylene.

Before recycle of said streams, carbon dioxide may be removed partiallyor completely, in a way as is for example discussed above with referenceto FIGS. 1 and 2.

The flow schemes of FIGS. 1 and 2 are equally applicable to the ethaneoxydehydrogenation embodiment of the present invention as describedabove, with the proviso that in the latter embodiment oxidizing agentshould not only be fed to ethylene oxide production unit 5 but also toethylene production unit 2 (the latter oxidizing agent feed is not shownin FIGS. 1 and 2).

The same advantages as described above apply to the ethaneoxydehydrogenation embodiment of the present invention.

An additional advantage of the ethane oxydehydrogenation embodiment ofthe present invention is that there is no need to remove remainingoxidizing agent, if any, from the product stream resulting from theethylene production step, because oxidizing agent is needed anyway inthe subsequent production of ethylene oxide. For example, US20100256432addresses the cumbersome requirement to eliminate unreacted oxygen froman ethane oxydehydrogenation product stream.

Further, advantageously, the same source of oxidizing agent as used forfeeding oxidizing agent to the ethylene oxide production step of thepresent process, can be used for feeding oxidizing agent to the ethyleneproduction step of the ethane oxydehydrogenation embodiment of thepresent process. This is illustrated in FIG. 3. For an explanation ofthe flow scheme of FIG. 3, reference is made to the above explanation ofthe flow scheme of FIG. 1, the only difference being that in the flowscheme of FIG. 3 there is an additional stream 15 comprising anoxidizing agent which is fed to ethylene production unit 2 and whichoriginates from the same source used for stream 4 comprising anoxidizing agent which is fed to ethylene oxide production unit 5.

In the ethylene production step of the above-mentioned ethaneoxydehydrogenation embodiment of the present invention, a streamcomprising ethane is contacted with an oxidizing agent, therebyresulting in oxidative dehydrogenation of the ethane into ethylene. Theoxidizing agent may be high-purity oxygen or air, but is preferablyhigh-purity oxygen which may have a purity greater than 90%, preferablygreater than 95%, more preferably greater than 99%, and most preferablygreater than 99.9%.

Further, it is preferred that the stream comprising ethane is contactedwith a catalyst. The catalyst may be a metal oxide catalyst, preferablya mixed metal oxide catalyst which is a metal oxide catalyst containingtwo or more different metals, preferably at most four or five differentmetals. Preferably, the catalyst is a pelletized catalyst, for examplein the form of a fixed catalyst bed, or a powdered catalyst, for examplein the form of a fluidized catalyst bed.

Examples of ethane oxydehydrogenation processes, including catalysts andother process conditions, are for example disclosed in U.S. Pat. No.7,091,377, WO2003064035, US20040147393, WO2010096909 and above-mentionedUS20100256432, the disclosures of which are herein incorporated byreference.

A suitable ethane oxydehydrogenation catalyst is a mixed metal oxidecatalyst containing molybdenum, vanadium, tellurium and niobium as themetals, which may have the following formula:

Mo₁V_(a)Te_(b)Nb_(c)O_(n)

wherein a is from 0.01 to 1, b is from >0 to 1, c is from >0 to 1, and nis a number which is determined by the valency and frequency of elementsother than oxygen. The nature of the ethane oxydehydrogenation catalystis not essential in terms of obtaining the advantages of the presentinvention as described herein.

The amount of the ethane oxydehydrogenation catalyst, if any, is neitheressential. If a catalyst is used, preferably a catalytically effectiveamount of the catalyst is used, that is to say an amount sufficient topromote the ethane oxydehydrogenation reaction. Although a specificquantity of catalyst is not critical to the invention, preference may beexpressed for use of the catalyst in such an amount that the gas hourlyspace velocity (GHSV) is of from 100 to 50,000 hr⁻¹, suitably of from200 to 20,000 hr⁻¹, more suitably of from 300 to 10,000 hr⁻¹, mostsuitably of from 500 to 5,000 hr⁻¹.

In the ethane oxydehydrogenation embodiment of the present invention,typical reaction pressures are 0.1-20 bar, suitably 1-10 bar, andtypical reaction temperatures are 100-600° C., suitably 200-500° C.

In general, the product stream resulting from the ethylene productionstep in the ethane oxydehydrogenation embodiment of the presentinvention comprises water in addition to ethylene and unconvertedethane. Water may easily be separated from said product stream, forexample by cooling down the product stream from the reaction temperatureto a lower temperature, for example room temperature, so that the watercondenses and can then be separated from the product stream.

Preferably, water is separated from the product stream resulting fromthe ethylene production step in the ethane oxydehydrogenation embodimentof the present invention, and the resulting product stream is then sentdirectly to the next step, that is to say the ethylene oxidation step.In this way, advantageously there is not any intermediate step, otherthan said water removal. Therefore, there is no need to separateethylene from unconverted ethane and/or to remove any carbon monoxide orcarbon dioxide prior to the ethylene oxidation step.

Preferably, at least part of the ethylene oxide is converted tomonoethylene glycol (MEG), which is a useful liquid product. Theconversion of ethylene oxide to MEG may be done using any MEG producingprocess that uses ethylene oxide. Typically the ethylene oxide ishydrolysed with water to MEG. Optionally, the ethylene oxide is firstconverted with carbon dioxide to ethylene carbonate, which issubsequently hydrolysed to MEG and carbon dioxide. The water is providedto the MEG zone as a feed containing water, preferably pure water orsteam. The MEG product is obtained from the MEG zone as a MEG-comprisingeffluent. Suitable processes for the production of ethylene oxide andMEG are described for instance in US2008139853, US2009234144,US2004225138, US20044224841 and US2008182999, the disclosures of whichare herein incorporated by reference.

The invention is further illustrated by the following Example.

EXAMPLE

In this experiment, ethylene was oxidized into ethylene oxide (EO) overa rhenium-containing catalyst prepared according to US20090281345 andhaving a silver content of 17.5 wt. %, using air as a source of oxygen(oxidizing agent), using ethane as ballast gas, and using ethyl chloride(EC) as moderator.

The experiment was performed in a “single-pass” or “once-through” modewithout any recycle. An inlet gas stream was contacted with the catalystin a U-shaped tubular steel microreactor that was immersed in atemperature-controlled molten metal bath. The inlet gas stream comprised25 vol. % of ethylene, 8.3 vol. % of oxygen, 0.6 vol % of carbondioxide, 260 parts per million by volume (ppmv) of EC, 32.3 vol. % ofethane, the balance comprising nitrogen originating from the air thatwas used as the source of oxygen and from the blend containing EC thatwas used as the moderator.

A gas flow rate of 254 cc/minute was directed through a 4.6 g charge ofcatalyst, providing a gas hourly space velocity (GHSV) of 2,850 hr¹.Total pressure was 16.5 bar gauge. Generation of 3.48 vol. % EO in theproduct stream corresponded to a work rate of 195 kg of product percubic meter of catalyst bed per hour (kg/m³/hr). The catalysttemperature to achieve said target work rate was 244° C.

Results of the experiment are shown in Table 1 below. The experimentshows that ethane can be used as a ballast gas in the oxidation ofethylene to EO. In addition, when using ethane as ballast gas, theselectivity of the ethylene oxidation reaction to EO is high.Furthermore, ethane is converted to only a small extent.

TABLE 1 Oxygen conversion 46.6% Ethylene conversion 15.2% Ethaneconversion 0.7% Selectivity of conversion of ethylene to EO 88.9%

1. A process for the production of ethylene oxide, comprising the stepsof: producing ethylene resulting in a stream comprising ethylene andethane; producing ethylene oxide by subjecting ethylene and ethane fromthe stream comprising ethylene and ethane to oxidation conditionsresulting in a stream comprising ethylene oxide, unconverted ethyleneand ethane; and recovering ethylene oxide from the stream comprisingethylene oxide, unconverted ethylene and ethane.
 2. A process accordingto claim 1, wherein unconverted ethylene from the stream comprisingethylene oxide, unconverted ethylene and ethane is recycled to the stepof producing ethylene oxide.
 3. A process according to claim 2, whereina stream comprising unconverted ethylene and ethane is separated fromthe stream comprising ethylene oxide, unconverted ethylene and ethaneand is recycled to the step of producing ethylene oxide.
 4. A processaccording to claim 1, wherein ethylene is produced from a feedcontaining ethane, and ethane from the stream comprising ethylene oxide,unconverted ethylene and ethane is recycled to the step of producingethylene.
 5. A process according to claim 1, wherein ethylene isproduced from a feed containing ethane, and ethane from the streamcomprising ethylene oxide, unconverted ethylene and ethane is recycledto the step of producing ethylene and to the step of producing ethyleneoxide.
 6. A process for producing ethylene oxide, comprising the stepsof: producing ethylene by subjecting a stream comprising ethane tooxydehydrogenation conditions resulting in a stream comprising ethyleneand unconverted ethane; producing ethylene oxide by subjecting ethyleneand unconverted ethane from the stream comprising ethylene andunconverted ethane to oxidation conditions resulting in a streamcomprising ethylene oxide, unconverted ethylene and unconverted ethane;and recovering ethylene oxide from the stream comprising ethylene oxide,unconverted ethylene and unconverted ethane.
 7. A process according toclaim 6, wherein a stream comprising unconverted ethylene andunconverted ethane is separated from the stream comprising ethyleneoxide, unconverted ethylene and unconverted ethane and is recycled tothe step of producing ethylene oxide.
 8. A process according to claim 6,wherein a stream comprising unconverted ethylene and unconverted ethaneis separated from the stream comprising ethylene oxide, unconvertedethylene and unconverted ethane, the stream comprising unconvertedethylene and unconverted ethane is separated into a stream comprisingunconverted ethylene which is recycled to the step of producing ethyleneoxide and a stream comprising unconverted ethane which is recycled tothe step of producing ethylene.
 9. A process according to claim 1,wherein at least part of the ethylene oxide is converted to monoethyleneglycol.
 10. A process according to claim 6, wherein at least part of theethylene oxide is converted to monoethylene glycol.